At this point, you are ready to test the dial-up connection. Select the
entry you just configured for multilink and start dialing. When prompted, enter
the correct username, password, and destination domain. The first time I used my
connection, I was surprised to hear both modems dial almost simultaneously.
When the RAS server answers the call, a notification box appears, informing
you that the second line is being bundled with the first. When both lines are
connected, the aggregate connection speed appears--it's really cool to see
55.2Kbps in place of 28.8Kbps. As I cruise the Internet, the transmit and
receive lights blink almost synchronously on both modems. The connection really
looks like one line, because the multilink protocol fragments and reconstructs
the packets traveling on this connection as a unit.
You can view this multilink connection in the Dial-Up Networking Monitor.
Select each line to see its connection speed. In the Summary view, the monitor
displays the connection with the name you defined for the dial-up entry. When
you expand the icon, the monitor displays each line individually.
Multilink Throughput
Next, I wanted to test throughput on the 55.2Kbps connection. At the
Microsoft FTP site, I used the native FTP command and a third-party GUI to
download a text file of just less than 500KB. With the native FTP command, my
throughput rate from Microsoft was 10.21Kbps. With the third-party GUI utility,
throughput was 10.18Kbps. Then, I downloaded a 1.2MB binary file from Microsoft
with the native FTP command--the download took 204 seconds with a transfer rate
of 6.24Kbps, which is closely matched by the third-party FTP utility. Last, I
downloaded a 700KB binary file that took 119 seconds and reported an overall
throughput of 5.92Kbps.
Download speed is difficult to evaluate fairly because so many factors are
unrelated to either modem speed or the speed of the system you are downloading
from. The biggest variable is the time of day. During my test, the highest
transfer rate was 10.21Kbps and the slowest was 4.38Kbps. During off-hours on a
single PPP connection, I got a maximum download speed from my Internet Service
Provider (ISP) of about 3.5Kbps; in my mind, a rate nearly double that speed
easily justifies an MPPP connection. Even when the Net slows down, the bundled
connection is nearly double the speed you get with a single line. MPPP certainly
makes browsing the Internet a lot more comfortable.
An MPPP connection can increase your download speed by more than 100
percent on small files and up to 100 percent on files that are more than 1MB.
The bad news is that very few ISPs support MPPP. Network vendors offer several
MP routers, but ISPs are not installing them for public access.
Another piece of bad news is that you cannot use MP with the callback
feature of a RAS client. The RAS server stores only one phone number for each
user, so only one modem can return the call.
However, I think MP is a good solution for branch offices that need a
faster connection to corporate, as long as you have two phone lines available
and an NT server at the corporate data center. MP does not require special
hardware, is cheaper than ISDN, and competes well with ISDN speeds, especially
if the modems at both ends are of the 56Kbps variety.